One type of hybrid vehicles is provided with an electrically controlled differential portion including a differential mechanism, connected to an engine in a drive-force transmissive state, whose differential state is controlled with controlling an operating state of a first electric motor, a second electric motor connected to a power transmitting path extending from the differential mechanism to drive wheels, and a mechanical shifting portion forming part of the power transmitting path. The differential mechanism includes a differential-action limiting device with which the differential mechanism can be selectively switched into one of a differential state enabling the differential action and a non-differential state disenabling the differential action. When starting up the engine, the control device operates to rotate the first and second electric motors utilizing the differential action of the differential mechanism for drivably rotate the engine for startup thereof.
Such a control device for hybrid vehicle drive apparatus is disclosed in, for instance, Patent Publication 1 (JP No. 2005-264762). Besides, Patent Publication 2 (JP No. 2003-193878) and Patent Publication 3 (JP No. 2006-2913) disclose technologies that are known in the art.
With such a hybrid vehicle drive apparatus disclosed in, for instance, Patent Publication 1, when the vehicle is driven with at least the engine to run at a high speed, if a vehicle occupant operates to switch a shift position from a “D” position to an “N” position, then, a provability takes place with a rapid drop occurring on a running load. Such a rapid drop in running load also takes place when the mechanical shifting portion has a large speed ratio with a fluctuation occurring in a decelerating direction.
Here, the running load acts in a direction to suppress an increase in rotation speed of the input shaft of the mechanical shifting portion. Thus, a rotation speed of a rotary element incorporated in the differential mechanism or the mechanical shifting portion, the second electric motor and associated engaging elements, connected to such component parts, rapidly increase, reaching high-speed rotations. This results in a likelihood of degradation occurring in durability of the rotary elements and the engaging elements.